1. Technical Field
This invention relates to a semi-closed fluid pumping method and apparatuses and, more precisely, to a system for removing floating hydrocarbon layers from the surface of groundwater.
2. Discussion
Various governmental regulations require monitoring of soil or groundwater quality in the vicinity of underground storage tanks (USTs) containing liquid hydrocarbons. In some cases, product releases or spills result in sufficient quantities such that a floating liquid layer may be detected. In response to this potential environmental risk, various means have been developed for release detection and product recovery. Prior art will show many devices for removing these floating liquid layers, known as "free product", from the groundwater. Most methods use pumps or labor intensive means.
For example, devices known as "filter canisters" can be installed in wells for early detection and recovery of free product. These devices are situated at or within the free product layer and groundwater interface. These devices are generally removed to monitor or to recover the free product. This becomes labor intensive in terms of the time required and the volume of product recovered. Such a discussion can be found in an article titled "Cutting the High Cost of Free Product Removal"--published in LUSTline (Bulletin 16, March 1992) which failed to recognize the extensive labor and time required to remedy the situation. Improvements to these devices include pumps to bring the collected liquids to a point at the surface. Most filter canister designs allow for some evaporation of volatile liquids as venting is required.
Other improved systems include a second pump used to lower the groundwater table creating a "cone of depression." This theory is meant to create a greater pressure gradient towards the recovery device which influences the mobile free product to migrate to this low point more quickly and in greater thickness. However, in this process the mobile free product is smeared through the soil creating a more widespread contamination of the soil, a greater product to water interface which increases groundwater contamination, a greater capillary fringe thereby reducing ultimate product mobility and ultimate final recovery, and removes naturally occurring bacteria which are important in the passive stages of soil and water decontamination. Furthermore, the pumped groundwater may require treatment before discharge. The ratio of groundwater pumped to product recovered is extremely high; on the order of 1,000:1 to 2,000:1.
Many devices will incorporate electronic sensors to control the overall process. Some systems, not always disclosed by Patents, discharge the pumped groundwater back to the aquifer at an up gradient location. This is known as a recharge system which will preserve some of the naturally occurring bacteria. However, many of these bacteria may still be destroyed by the pumping action.
Many devices inadvertently collect water in conjunction with a liquid hydrocarbon recovery process which may require separation, treatment or disposal of the recovered liquids. In some devices, a filter media or membrane is used to absorb or filter the hydrocarbons which may foul with microscopic bacteria, known as bio-fouling, and fail to collect floating product at all.
Yet in other devices, air is used to assist product recovery which results in volatile organic compound (VOC) emissions to the atmosphere and further treatment may be needed. VOC emissions also occur with the pumping of volatile liquids into vented containers. Few if any of theses devices offer "closed to the atmosphere" storage. Loss of constituents is very important in the analysis of chemical releases. For example, U.S. Pat. Nos. 2,457,851, 2,515,569, 2,520,056, and 2,770,492 show the moving transferring, supplying or dispensing of liquids to a lower level without filtering or separation. U.S. Pat. Nos. 622,088, 622,562, 4,280,658, 4,759,857, 4,761,226 filter or separate liquids to a lower level. None of these devices are closed siphons and none take advantage of the upper portion of the siphon.
In U.S. Pat. Nos. 3,669,275, 243,529, 4,243,529, 4,273,650, 4,663,037, 4,872,994, and 4,998,585 pumps are used to remove the floating liquid layers to an elevated location.